In general, a CMOS sensor is a solid-state imaging apparatus including a two-dimensional pixel array having pixels. Each pixel includes a photoelectric transducer for generating signal charge in response to an incident light beam and pixel transistors for converting the signal charge to an electrical signal and for outputting this electrical signal. The CMOS sensor reads individual pixel signals through a plurality of vertical signal lines provided corresponding to individual columns of pixels and processes the read pixel signals to output the processed signals to an output unit through a horizontal signal line.
The CMOS sensor can randomly access the individual pixels by selectively scanning the pixels and signal-processing circuits.
Color filters having a predetermined array pattern are provided on the pixel array to convert an incident light beam on the sensor to light beam components having respective colors. These light beam components enter the respective pixels, and color images are captured.
A known CMOS sensor has a higher reading rate than a CCD sensor, but has only one horizontal signal line. This structure limits a further increase in the reading rate of the known CMOS sensor.
To solve this problem, an attempt to achieve a higher reading rate has been made by increasing the number of horizontal signal lines.
FIGS. 5A and 5B are schematic views illustrating the signal-outputting operation with a certain color arrangement in a pixel array and two horizontal signal lines. In this example, the two horizontal signal lines are dedicatedly assigned to respective pixel columns of the pixel array.
As shown in the drawings, the color arrangement in the pixel array 1 alternately includes RGr rows (the (2n)th row) and GbB rows (the (2n+1)th row). Each RGr row alternately includes red (R) pixels and green (Gr) pixels, and each GbB row alternately includes green (Gb) pixels and blue (B) pixels. In the drawings, the asterisks (*) indicate rows to be read, and the rows are sequentially selected from the top to the bottom.
In FIG. 5A, the (2n)th pixel row is selected, R pixel signals are output to an output system A through a horizontal signal line 2A, and Gr pixel signals are output to an output system B through a horizontal signal line 2B.
In FIG. 5A, the (2n+1)th pixel row is selected, Gb pixel signals are output to the output system A through the horizontal signal line 2A, and B pixel signals are output to the output system B through the horizontal signal line 2B.
However, in the known method for reading pixel signals described above, the Gb pixel signals and the Gr pixel signals that have the same color are separately output to the respective output systems A and B, as shown in FIGS. 5A and 5B. Thus, though the same color in an object is captured through respective color filters, color difference may occur between the pixel rows due to variance in characteristics of, for example, transistors in the different systems. Such color difference generates horizontal stripes.
Since the solid-state imaging apparatus is a high-precision analog circuit processing signals, a slight change in the characteristics of transistors changes the characteristics of pixel signals. Especially, a change in the characteristics of horizontal signal lines causes horizontal stripes that periodically appear when signals are output from all pixels.
This type of problem does not occur when signals are transmitted through a single horizontal signal line. However, the problem may occur when the number of horizontal signal lines is increased to achieve a high reading rate.
It is an object of the present invention to provide a solid-state imaging apparatus and a method for reading signals therefrom that can read pixel signals separately through a plurality of horizontal signal lines at a high reading rate and that can eliminate, for example, color difference in image signals and stripes.